This invention relates to an apparatus and method for alleviating pressure between the print head the resilient roller of thermal printing mechanisms when printing is not taking place. In particular, the method involves the use of a cam means, such as a lever, for camming apart the surface of the print head and the resilient roller.
It is generally known that thermal printing mechanisms including a resilient roller for pressing thermally sensitive paper against a thermal print head in order to achieve a visual effect (usually an alphanumeric printout) on the paper. The print head typically contains minute resistors arranged in a row and positioned so that they come into contact with the paper along a line which is substantially perpendicular to the direction of movement of the paper during operation of the printing mechanism. When an electrical current is passed through the resistors, the heat generated therefrom produces small dot images on the thermally sensitive paper. In order to create the desired printout, the number and location of dots to be printed in each row, and the longitudinal velocity of paper movement along the print head, are properly selected, usually under microprocessor control.
However, conventional thermal printing mechanisms are not completely satisfactory. Because there is considerable pressure between the print head and the resilient roller, a flat may be formed on the roller at points of contact with the print head. If the printing mechanism is not operated for a considerable length of time, the flat may become permanent, and as a result, print quality will be less than desirable. Yet in some applications, long periods of inactivity may be desirable or even required.
Accordingly, it is an object of the present invention to provide a thermal printing mechanism which does not produce flats on the resilient roller when not operated for any length of time.
Still other objects and advantages of the invention will, in part, be obvious and will, in part, become apparent from the following specification.